1. Field of the Invention
The present invention relates to an insert for use in a long product such as a weather strip for a motor vehicle, which is formed by extrusion and used to provide a seal between a door member such as a vehicle door, a trunk lid, etc., and an opening in a vehicle body, a method for producing such an insert, and a method for producing such a long product provided with such an insert.
2. Description of Related Art
As shown in FIG. 1, a long product such as a weather strip 10 for a motor vehicle is attached to a periphery around an opening in a vehicle body. The weather strip 10 has a trim portion 12 with a generally U-shaped cross-section, as a base portion for attachment to a flange, and a tubular seal portion 14 for contacting a door member and providing a seal between the vehicle body and the door member. An insert 16 produced by subjecting a band-shaped metallic plate to punching is embedded in the trim portion 12 for enlarging the gripping force of the trim portion 12 (see Publication of Japanese Utility model application No. sho 55-8168, for example).
As shown in FIG. 2, the insert 16 has a ladder-like configuration, and is composed of a large number of insert pieces 18, each extending in a widthwise direction of the insert 16. The insert pieces 18 are joined to each other in their both ends with joining parts extending in a longitudinal direction. The joining parts include first joining parts 20, each having a smaller width so as to be readily breakable, and second joining parts 22, each having a larger width so as to be difficult to break. The first joining parts 20 and the second joining parts 22 are alternately arranged in a longitudinal direction of the insert 16. The first joining parts 20 and the insert pieces 18 define first slits 24, whereas the second joining parts 22 and the insert pieces 18 define second slits 26.
When the long product is produced by feeding the insert 16 to an extruder and forming a covering layer of a rubber-like elastic body around the insert 16, the joining parts of the insert 16 remain joined for facilitating taking up of the same. But, when the long product is used to be attached along corners of the flange, etc., the joining parts are separated for enhancing the flexibility of the trim portion 12.
And after extrusion, the first joining parts 20 of the insert 16 are broken and separated, and consequently, there exist in the trim portion 12, a plurality of pairs of insert pieces 18, each being joined on an upper side and a lower side thereof with the second joining parts 22, thereby defining the second slits 26.
The insert 16 disclosed in this publication, is formed by subjecting a band-shaped metallic plate to punching, etc. so that parts of the metallic plate corresponding to the first slits 24 and the second slits 26 become wasted to produce metal scrap, thereby increasing the production costs. In addition, the thickness of the first joining parts 20 is identical to that of the remaining parts so that they have been difficult to be broken. The flexibility of the trim portion 12 is improved by breaking all joining parts, but in order to bend and break all joining parts, a long process is required to deteriorate productivity. And where the width of the joining parts is made smaller for facilitating braking thereof, there occurs the problem that the joining parts may break during the extruding step of the covering layer.
In order to overcome this problem, as shown in FIG. 3, first cut lines 28 with a long length and second cut lines 30 with a short length are alternately formed in a belt-shaped metallic plate 32 with uncut portions remained on both side ends thereof. In addition, side cut lines 34 are formed along side edges of the belt-shaped metallic plate 32. Thereafter, the uncut portions adapted to form the joining parts are subjected to rolling. As a result, openings of the long first cut lines 28, the short second cut lines 30 and the side cut lines 34 are enlarged to form first slits 36 and second slits 38, each having a width of C in FIG. 4, whereas uncut portions define first joining parts 40, each having a width of A shown in FIG. 4, and second joining parts 42, each having a width of B shown in FIG. 4 (see Publication of Japanese Patent application No. Sho56˜91931, for example).
In this case, as shown in FIG. 4. in a resultant insert 44, only the uncut portions are rolled in a longitudinal direction and elongated by a rolling amount so that the width of the first slits 36 and that of the second slits 38 are approximately identical to each other, and have not been enlarged furthermore. Where the rolling amount is increased, there occurs the problem that the insert 44 may be broken upon extruding the covering layer. For these reasons, the ratio of the width of the insert pieces 46 (D in FIG. 4) in the insert 44 becomes large, and the number of the insert pieces 46 per unit length increases so that the weight of the insert member 44 enlarges not to respond to the demand to reduce the weight of vehicle bodies.